A healthy intervertebral disc is flexible enough to allow movement between adjacent vertebrae or between a vertebra and another adjacent spinal column element, such as the coccyx (the most inferior portion of the vertebral column, resulting from the fusion of the four coccygeal vertebrae) and the sacrum (a triangular bone that is the posterior skeletal element forming the pelvis, formed by 5 fused vertebrae). This movement accommodates bending of the spine. Disease or degeneration of the tissues of a natural intervertebral disc often leads to intense pain and reduced mobility. When degeneration or disease of the natural intervertebral disc has progressed to the point where non-operative care such as medication, injections, and/or physical therapy is ineffective, surgical intervention may be required.
A common procedure for treatment of degenerative or diseased intervertebral discs involves removal of the natural tissues of the disc and fusion of the adjacent vertebrae. Fusion eliminates the mobility between the adjacent vertebrae, however, and can transfer stresses and movements to the intervertebral discs above and/or below the point of fusion.
Intervertebral disc prostheses have been developed to mitigate some of the problems caused by intervertebral fusion. In particular, various designs of intervertebral disc prostheses can provide a relatively normal range of movement to the adjacent vertebra, resulting in a more normal distribution of stresses and movements along the various segments of the spine. Intervertebral disc prostheses typically are configured to restore normal disc height, and can decrease surgical morbidity and complications from postoperative immobilization instrumentation typically present in fusion procedures.
U.S. patent application Ser. Nos. 10/476,565, 10/533,846, 11/051,710, and 11/362,253, each of which is assigned to the assignee of the present application and each of which is incorporated herein by reference for all purposes, disclose various intervertebral disc prosthesis configurations. In many of these configurations, the prosthesis may have an upper plate supporting the upper vertebra, a lower plate supporting the lower vertebra, and a mobile core or nucleus that provides some range of articulation between the upper plate and the lower plate.
Prior to the surgical implantation procedure, measurements often are made of the plates of the upper and lower vertebrae to confirm the viability of the procedure. Following discectomy in various representative procedures, the depth and width of the intervertebral space are measured, and a determination is made of an appropriate vertical spacing of the adjacent vertebra and the sizes of the upper and lower disc prosthesis plates and the core.
Typically, there are several selections for the depth and width of the intervertebral prosthesis plates and for the height of the core, depending on the type of intervertebral disc prosthesis. For example, the LDR Medical Mobi-C™ cervical disc prosthesis currently can be configured with any of 4 plate sizes and 3 core heights, and the LDR Medical Mobidisc™ lumbar disc prosthesis currently can be configured with any of 18 plate sizes and 6 core heights. In addition, the surgeon may wish to accommodate or correct a lordosis or kyphosis by using one or more plates having an angular offset between the vertebral axis implied by a normal to the plate's vertebral contact surface and a mean, or neutral, normal axis implied by the plate's core contact surface. Thus, even within a single product line, there may be numerous combinations of individual disc prosthesis elements available to suit the requirements of a particular patient.
In various intervertebral prosthesis product systems, the upper plates, the lower plates, and the cores are provided to the sterile field of the surgical suite individually. Once the proper configuration of the upper plate, the lower plate, and the core has been determined, typically the surgical staff must acquire the proper upper plate, lower plate, and core from inventory.
The components of the prosthesis typically are then assembled for mounting with or loading into a prosthesis insertion tool, or assembled directly with the insertion tool. In some systems, an assembly stand or jig is used for assembling the prosthesis components and loading the assembled prosthesis into an insertion tool. The selection and assembly process can be time consuming and awkward, potentially resulting in delays during the surgical proceeding. Handling of the components during assembly process can compromise the sterility of the prosthesis, and the use of additional handling equipment, such as an assembly stand or jig, can require further sterilization procedures, increase the complexity of the procedure, and clutter the surgical suite.
In some systems, an assortment of insertion tools are each configured for use with a single size or a limited range of sizes of the various prosthesis component combinations. Generally, the required size and configuration of the various prosthesis components will not be known until the surgical procedure has commenced. Thus, the surgeon will have to select the proper insertion tool during the procedure, following the determination of the proper sizes and configurations of the various prostheses components. The surgical staff therefore must disinfect and sterilize several insertion tools to have a full selection of the insertion tools at hand during the procedure. During the procedure, selection of the appropriate tool and confirmation of the selection will add to the duration and complexity of the surgical procedure. In various designs of insertion tools, however, the operative components of the insertion tool body are the same regardless of the prosthesis configuration, and only the tool's insertion adapter (for example, a head, holder, or other carrier of the assembled prosthesis) differs among the various insertion tools. Often, the differences among the various insertion adapters are dictated solely by the differences in sizes and configurations of the prosthesis components.